Excuse me if I'm being particularly inept this morning, but can anyone offer
any help on the following problems please?
Inverse of IntegerDigits
========================
I'm playing around with some binary numbers, and am using IntegerDigits
to convert from a decimal integer to the binary notation. eg.
In[1]:= IntegerDigits[10,2]
Out[1]= {1,0,1,0}
What is the function to convert back? eg. I want to do
In[2]:= DigitsToInteger[{1,0,1,0},2]
and get
Out[2]= 10
I've scoured the manual and can't find the function. This led me to
try to write my own function, which identified another problem...
"Index" Function
================
Writing a function to convert back is easy in principle, eg.
DigitsToInteger[x_,n_] := Apply[Plus[Map[(#*n^(Index[#]-1))&, Reverse[x]]]]
would do the trick, but I seem to require a function, that I've called
Index[] here, that when Map[]'d across a list returns the position of
each element. Thus I want a function that works as follows:
In[3]:= Map[Index[#]&, {2,6,3,9,10,2,4}]
Out[3]= {1,2,3,4,5,6,7}
But I can't seem to find this function either!
For the moment I'm using the following more Fortran-like function, which
works, but disturbs my sensibilities:
DigitsToInteger[x_,n_] :=
Module[{int=0, l},
l = Reverse[x];
Do [int = int + 2^(i-1)*l[[i]],
{i, Length[i]}
];
int
]
Any suggestions?
Paul E Howland Tel. +44 (0)1684 895767
Long Range Ground Radar Sensors Fax. +44 (0)1684 896315
LSC2 Division Email. PEHOWLAND at DRA.HMG.GB
Defence Research Agency
St Andrews Road
Malvern
Worcestershire, WR14 3PS, UK
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